Numerical Simulation of Drainage of Permeable Friction Course Considering Surface Runoff and Seepage Flow

Standing water on the pavement surface during rainy days is one of the major causes of roadway crashes. Permeable (sometimes porous is used instead of permeable) friction course (PFC) overlays have been installed on selected roadways to assist water drainage to make roadways safer. However, the drainage capacity under different rainfall events for different roadway configurations has not been fully, systematically assessed yet. In this paper, an existing numerical modeling framework to couple the surface runoff and porous-medium seepage was customized to model for drainage of PFC pavement under different rainfall events, which was calibrated by the test data of large-scale PFC testing under different rainfall events. The numerical model coupled the two-dimensional (2D) surface runoff and the three-dimensional (3D) porous-medium flow with the use of a soil constitutive model from the literature. The surface runoff was represented by 2D shallow-water equation to mimic water runoff and possible ponding at the pavement surface, and 3D porous-medium flow based on Richard's equation was used to simulate the subsurface water seepage through PFC pavement under saturated and unsaturated conditions. The surface water flow and subsurface seepage were coupled based on the principles of momentum reservation and mass balance. The hydraulic conductivities of PFC pavement were determined as a function of void ratio through large-scale tests. The van Genuchten parameters n and α were determined through simulation of a large-scale test that was completed at a section of 2.1×14.63-m2 sloped PFC pavement in the lab. The numerical model with calibrated parameters was utilized to evaluate the possible water accumulation at the pavement during different rain intensities. The parametric study conducted based on this developed numerical model indicated that PFC pavement was effective to remove surface water timely for most of rainfall events except for rainfall events greater than very heavy level. However, the numerical further suggested that pavement slope would assist PFC to further facilitate water flow under very heavy rainfall events.